Originally Posted By pc-ops:there is always a armchair builder tossing hate because they cant build something nice.

Sort of like SLR building their 7.5 308. someone had to up my 10.5. I have my 7.5 with a surefire warden still rattles your teeth but nothing like my 308

would love to see a pic of it. and 5" barrel anyone on the receiving end isn't going to critique the build

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No hate...and no inability.
Just a question of usage.
If it is just a range toy to punch paper, or shoot water jugs in front of a dirt berm, or just to post on the web, then yeah...have a blast. It is your money, do what you want. Ballistics and function are secondary concerns...it is just a cool toy.

If it is designed to be a true PDW, then it is still your money, but ballistics and function are (or should be) legit questions.

Are you building the best PDW you can build as compact as possible, or are you building the shortest 5.56 AR you can build, and calling it a PDW? Those are mutually exclusive.

Since this is a pistol sub-section, my assumption is that these are all pistols, and most of the posters ALSO have true handguns...be it open or concealed carry. Is this PDW being built so short because it is ACTUALLY being carried daily? Is it replacing a daily carry handgun?
Or is this a weapon that will be kept in a back-pack, travel bag, suitcase, laptop bag, etc...and kept under a bed, in a closet, in a foot-locker and such? Something that you can quickly get to in the middle of the night, or grab and throw in a vehicle, but does NOT replace your daily carry handgun? I ask because if it is the latter...why give up some much range, energy and function over a couple of inches and a caliber (if it isn't something that is being carried daily)?

I'd be curious how the 45gr Barnes would behave in a super short barrel.

I'll also be curious what kind of velocities we can get from the 350 Legend in super short barrels. There's something to be said for swept volume.

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@RDTCU
That bullet is on the top of my list to try from a 5" barrel. QL Predicts ~2300 ft/sec and increases almost 100ft/sec per 1/2" till about 7" then tapers off(which has been very conservative from my testing with other bullets in my 6" .223 short)

I designed a PDW cartridge that i'm hoping will feed from standard mags. Just machined my die last weekend and plan to start the testing this weekend if all works out.
With the cartridge on the left (.223 short) I'm getting 2700 ft/sec from a 40gr cup and core bullet in a 6" barrel but the excessive case taper was not AR mag friendly. would likely work great in ppsh 43 mags.
The 22 Mamba (right) un-fireformed is .9gr greater case capacity. both rounds are formed from .223 rem. The 22 Mamba is also sporting a .223 wylde throating so I plan on upping the pressure on it as well.

Once I get it all sorted out I plan on trying the LR-300 operating system and if I succeed i'll stamp a second lower and make a true folder.

How is OP's "PDW" better than just getting an off the shelf FN FiveseveN pistol with some 30 round magazines and feeding SS197 JHP (1950 fps) or actual SS190 AP (2350 fps). Or even SBRing an FN PS90? The pistol is pistol sized and the P90 SBR will still be shorter than even a 1" AR15.

How is OP's "PDW" better than just getting an off the shelf FN FiveseveN pistol with some 30 round magazines and feeding SS197 JHP (1950 fps) or actual SS190 AP (2350 fps). Or even SBRing an FN PS90? The pistol is pistol sized and the P90 SBR will still be shorter than even a 1" AR15.

How is OP's "PDW" better than just getting an off the shelf FN FiveseveN pistol with some 30 round magazines and feeding SS197 JHP (1950 fps) or actual SS190 AP (2350 fps). Or even SBRing an FN PS90? The pistol is pistol sized and the P90 SBR will still be shorter than even a 1" AR15.

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How is it not better? My 7.5" pistol can (in a pinch at least)
1) Use any ammo any of my other (or 100 million other) rifles can use
- 1b) Any of my rifles can use its ammo should it fail in use
2) Use any spare part for any of my other (or 100 million other) rifles can use
- 2b) Any of my rifles can use parts from it should they need them
3) Be instantly used by anyone already familiar with the AR platform
4) Allow me to take an AR platform gun in situations where an AR wouldn't be otherwise allowed

I mean, seriously.. how can you argue with a pistol that shares everything with your rifles, requires no special parts, and is still plenty lethal in the range you expect to use a pistol.

How is OP's "PDW" better than just getting an off the shelf FN FiveseveN pistol with some 30 round magazines and feeding SS197 JHP (1950 fps) or actual SS190 AP (2350 fps). Or even SBRing an FN PS90? The pistol is pistol sized and the P90 SBR will still be shorter than even a 1" AR15.

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FN PS90s are spendy. Then you get to add a $200 tax stamp and then pay for a relatively hard to find specialty ammo that only runs in a handful of firearms. Further the PS90 can be hard to find and who knows when/if FN ends up pulling civilian production altogether. Also, as I noted many, many times ballistically speaking the 556 out of a short barrel is similar if not outright superior to 5.7 in a similar barrel. Then there's the consideration that the 7 inch AR15 is about the same size and weight as a HK MP7 while beating the 4.6 cartridge ballistically.

7 inch AR can be run as a pistol, fires a cartridge that is both ubiquitous and comes in a plethora of loadings/projectile types, is easier to reload than the so-called PDW cartridges, and outperforms them. Meanwhile parts are commonly found and share commonality with all your other AR15s so you get a substantial amount of customization choices while keeping parts relatively cheap in comparison to the FN 5.7 offerings. I am not even going to get started on magazine advantages.

I cannot find a single advantage a semi-auto FN PS90 has over an AR15 with the same barrel length for us regular joes other than flexing on the poors. With a drum mag on the AR the PS90 doesn't even have a capacity advantage.

The FN FiveseveN isn't even close to being a PDW, the already questionable 5.7 is even more anemic out of that short barrel, then you only have your single contact point whereas the AR has three. It's best advantage is capacity versus other handguns. Against a rifle? Zero outside of concealability.

Just because you don't understand something doesn't mean it doesn't make sense.

Originally Posted By codifier:. FN PS90s are spendy. Then you get to add a $200 tax stamp and then pay for a relatively hard to find specialty ammo that only runs in a handful of firearms. Further the PS90 can be hard to find and who knows when/if FN ends up pulling civilian production altogether. Also, as I noted many, many times ballistically speaking the 556 out of a short barrel is similar if not outright superior to 5.7 in a similar barrel. Then there's the consideration that the 7 inch AR15 is about the same size and weight as a HK MP7 while beating the 4.6 cartridge ballistically.

7 inch AR can be run as a pistol, fires a cartridge that is both ubiquitous and comes in a plethora of loadings/projectile types, is easier to reload than the so-called PDW cartridges, and outperforms them. Meanwhile parts are commonly found and share commonality with all your other AR15s so you get a substantial amount of customization choices while keeping parts relatively cheap in comparison to the FN 5.7 offerings. I am not even going to get started on magazine advantages.

I cannot find a single advantage a semi-auto FN PS90 has over an AR15 with the same barrel length for us regular joes other than flexing on the poors. With a drum mag on the AR the PS90 doesn't even have a capacity advantage.

The FN FiveseveN isn't even close to being a PDW, the already questionable 5.7 is even more anemic out of that short barrel, then you only have your single contact point whereas the AR has three. It's best advantage is capacity versus other handguns. Against a rifle? Zero outside of concealability.

Just because you don't understand something doesn't mean it doesn't make sense.

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This thread needs moar @PursuitSS

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I'm going to be the last person to argue that 5.7x28 is better than 5.56x45 (it isn't)

But when you consider the mission for a true "PDW" the AR fails miserably.

IMHO, a PDW must be...

Light
DAMN SHORT AND COMPACT
100% reliable
Ergonomic
Ambidextrous
High capacity
Able to be used effectively with one hand (EITHER hand!)

As far as I'm concerned the main failing of the FN P90/PS90 is the difficulty in rapidly changing magazines.

As to capability of the weapon, I can shred a B26 silhouette with our P90 on full auto one handed, I can't do a 50 rd "mag dump" one handed but I can stay on target for around 10 rd bursts.

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in the case of OP's configuration, an SBR PS90 would be both longer and heavier. He has described it as 100% reliable so far and AR15 is known for being ergonomic and is operationally ambidexterous. So really the only way in which a P90 would fit your definition of a PDW better than OPs AR is in the one handed operation category.

I’m going to be the last person to argue that 5.7x28 is better than 5.56x45 (it isn’t)

But when you consider the mission for a true “PDW” the AR fails miserably.

IMHO, a PDW must be...

Light
DAMN SHORT AND COMPACT
100% reliable
Ergonomic
Ambidextrous
High capacity
Able to be used effectively with one hand (EITHER hand!)

As far as I’m concerned the main failing of the FN P90/PS90 is the difficulty in rapidly changing magazines.

As to capability of the weapon, I can shred a B26 silhouette with our P90 on full auto one handed, I can’t do a 50 rd “mag dump” one handed but I can stay on target for around 10 rd bursts.

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If we're going to admit that "no way in hell" that an AR isn't a PDW, then you have to hold the PS90 to the same standard. According to the definition of a PDW nothing a civilian can own right now counts; AFAIK the 5.7 and 4.6 offerings came after the Hughes amendment, and PDWs require select fire. In fact, the whole point of a real PDW is that they make up for relatively shitty cartridge power with volume, really just a submachine gun that was designed to be lighter, higher capacity, lower recoiling, and theoretically better cartridge performance.

So just to be clear, when anyone says PDW, they really just mean a really small gun that isn't a handgun per se when it comes to us less equal animals. Given that HK has deigned to not bless us with MP7s or anything else chambered in 4.6 and FN has deemed that only the highly expensive and hard to find PS90 and its almost-as-expensive little sibling pistol be the only offerings for 5.7 those cartridges are really out of the discussion leaving standard rifle or pistol rounds.

Thus, anything not LEO/MIL (government) isn't going to get a true PDW and thus everything is a kind of wannabe analog to the real thing.

Many of the things you have listed are either completely subjective, or can be applied to both a PS90 and short barreled AR (pistol or SBR). The biggest objectionable quality the PS90 has (assuming its SBRd) is that it can be very short comparatively.

Don't get me wrong, if it were up to me there'd be real PDWs for everyone, just like real Assault Rifles. I also am a fan of bullpups, but FN and HK really aren't doing themselves any favors making them as widespread and competitive as the AR pattern rifles; and for most people the short ARs are going to have way more going for them for the """""""""PDW"""""""" role.

I’m going to be the last person to argue that 5.7x28 is better than 5.56x45 (it isn’t)

But when you consider the mission for a true “PDW” the AR fails miserably.

IMHO, a PDW must be...

Light
DAMN SHORT AND COMPACT
100% reliable
Ergonomic
Ambidextrous
High capacity
Able to be used effectively with one hand (EITHER hand!)

As far as I’m concerned the main failing of the FN P90/PS90 is the difficulty in rapidly changing magazines.

As to capability of the weapon, I can shred a B26 silhouette with our P90 on full auto one handed, I can’t do a 50 rd “mag dump” one handed but I can stay on target for around 10 rd bursts.

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Given some folks have gotten ARs down to under 4 lbs, I'd say an AR could make a good PDW. That was the original intent of the XM-177 in the first place. The 5.7x28mm is an interesting round, but when 5.56x45mm is ubiquitous, it doesn't make a whole lot of sense to change to a different cartridge when you can just make the base gun lighter and shorter.

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I have the benefit of having access to a P90, after THOUSANDS of rounds down range out of our P90 and our M-16’s I can definitely state for 100 yards or less I’m going to go with the FN P90 over the M-16.

For longer ranges the M-16 makes a lot more sense, but we are talking about PDW’s.

I’ve yet to see an M-16 with a barrel shorter than 10.5” that I’d take into harms way. The dependability goes in the shitter on 7.5” and shorter.

And as to an M-16 being fully ambidextrous, it’s not even in the same ballpark as a P90. The same comment on ergonomics.

"When trading bullets it is better to give than to receive" _____________________

"People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf." - George Orwell

I have the benefit of having access to a P90, after THOUSANDS of rounds down range out of our P90 and our M-16’s I can definitely state for 100 yards or less I’m going to go with the FN P90 over the M-16.

For longer ranges the M-16 makes a lot more sense, but we are talking about PDW’s.

I’ve yet to see an M-16 with a barrel shorter than 10.5” that I’d take into harms way. The dependability goes in the shitter on 7.5” and shorter.

And as to an M-16 being fully ambidextrous, it’s not even in the same ballpark as a P90. The same comment on ergonomics.

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And that's fine, you do you. No one can or should say that you should go with one or the other.

However, don't shit all over others' choices. The short barreled AR has its pros/cons, as does the PS90. For many people, the AR has a lot more going for it.

I also must note that you as a private citizen won't ever own a P90, and you will likely not own an M-16 either (unless you got tens of thousands of dollars to invest). So your anecdotes with those don't really apply here; 90% or more people on this board won't get to own them either.

I also must note that you as a private citizen won't ever own a P90, and you will likely not own an M-16 either (unless you got tens of thousands of dollars to invest). So your anecdotes with those don't really apply here; 90% or more people on this board won't get to own them either.

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But I do own a FN P90 and a few M-16’s as an S.O.T.

"When trading bullets it is better to give than to receive" _____________________

"People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf." - George Orwell

I don't know where we could find an "official" definition of what a PDW is or is not, but AAC calls the honey badger a PDW, Maxim calls their new 556 a PDW, FN calls the SCAR 16S a PDW, and either Barrett or LWRC makes a 6.8 piston AR that they market as a PDW.

Glad you like your 4.75 inch AR I’m sure it would suck to be shot with it. I would say it fits the role of a PDW. A lot of people get hung up on type classifying firearms. Must be select fire , must use THIS Ammo, must say PDW on the weapon.

Originally Posted By gungrass:Oh how I would love a KAC PDW....it does look kinda ARish....I think I’ll start calling all my guns Personal Defense Weapons.

Glad you like your 4.75 inch AR I’m sure it would suck to be shot with it. I would say it fits the role of a PDW. A lot of people get hung up on type classifying firearms. Must be select fire , must use THIS Ammo, must say PDW on the weapon.

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Agreed. I never liked the so called "PDW" marketing term. They are all useful in a self defense situation. Some calibers might not be the best tool but any firearm in hand is better than nada when the SHTF. YMMV.

That said my 8.3 barreled 300blk pistol would be my "PDW" I suppose. If the SHTF at my place that is the one I'm going for as I keep my suppressor on it for that very reason as I'd effectively be in a CQB situation defending the casa.

Originally Posted By gungrass:Oh how I would love a KAC PDW....it does look kinda ARish....I think I’ll start calling all my guns Personal Defense Weapons.

Glad you like your 4.75 inch AR I’m sure it would suck to be shot with it. I would say it fits the role of a PDW. A lot of people get hung up on type classifying firearms. Must be select fire , must use THIS Ammo, must say PDW on the weapon.

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The Personal Defense Weapon concept has a meaning and definition behind it. The idea was for a replacement for submachinegun's relatively lackluster performance; particularly against soft body armor while still maintaining its benefits namely ease of use, compactness, and low recoil. The idea was that SMGs were outdated WW2 tech and that we could do better with modern (in the 90s anyway) technology; thus came the MP7 and P90s with their miniaturized rifle cartridges. They were never meant to replace an infantryman's carbine, and like their older SMG brothers relied on volume of fire as a component of their effectiveness. This is why they needed to be low recoiling and carry a substantial amount of ammo; rear echelon troops could theoretically carry these rather than a pistol (very ineffective in a war zone), SMG (see previous, but slightly better), or carbine (too heavy, hard to use, expensive, so-on, so-on).

Point is that the PDW concept has a defined rationale behind it, it is very fashionable right now to call things names that they aren't; you will see that with all the different military rifle "clones" out there that only have a passing semblance to what the person supposedly modeled them after yet gets defensive if someone says "hey, that's really not a M4gery, you got a 20 inch barrel, and PDW stock on it". Words have meaning for a reason, otherwise you can't get pissed if someone calls your wife a slut because she has sex with men because that's "close enough". That said I do see your point, but understand there is a reason I stressed earlier that technically none of us own a real PDW, we just have semi-auto rifle/pistols that we try to fill that role with albeit without all the features we would like. But you should care about how words are used because antis love your stance: look at their abuse of the term Assault Rifle. They have bastardized that into "Assault Weapon" to demonize anything they don't like.

Originally Posted By codifier: The Personal Defense Weapon concept has a meaning and definition behind it. The idea was for a replacement for submachinegun's relatively lackluster performance; particularly against soft body armor while still maintaining its benefits namely ease of use, compactness, and low recoil. The idea was that SMGs were outdated WW2 tech and that we could do better with modern (in the 90s anyway) technology; thus came the MP7 and P90s with their miniaturized rifle cartridges. They were never meant to replace an infantryman's carbine, and like their older SMG brothers relied on volume of fire as a component of their effectiveness. This is why they needed to be low recoiling and carry a substantial amount of ammo; rear echelon troops could theoretically carry these rather than a pistol (very ineffective in a war zone), SMG (see previous, but slightly better), or carbine (too heavy, hard to use, expensive, so-on, so-on).

Point is that the PDW concept has a defined rationale behind it, it is very fashionable right now to call things names that they aren't; you will see that with all the different military rifle "clones" out there that only have a passing semblance to what the person supposedly modeled them after yet gets defensive if someone says "hey, that's really not a M4gery, you got a 20 inch barrel, and PDW stock on it". Words have meaning for a reason, otherwise you can't get pissed if someone calls your wife a slut because she has sex with men because that's "close enough". That said I do see your point, but understand there is a reason I stressed earlier that technically none of us own a real PDW, we just have semi-auto rifle/pistols that we try to fill that role with albeit without all the features we would like. But you should care about how words are used because antis love your stance: look at their abuse of the term Assault Rifle. They have bastardized that into "Assault Weapon" to demonize anything they don't like.

Words have meaning for a reason.

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You fell into your own trap. Historically, infantrymen have never carried carbines - they carried rifles. Everyone else carried carbines, the carbine being a shorter version of the infantry rifle - the PDW of the day. Meanings change, and usage changes. Infantry now carry carbines - the weapon that was intended as a PDW for everyone else.

Now that the infantry rifle is a carbine, just about anything smaller will fall into the PDW category - and have shorter effective range, just like the shortcomings of carbines historically compared to the standard infantry rifle.

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I have read all this about stopping power, penetration, and etc. Made me think, wonder how well a 40 grain 22 hornet bullet would perform in one of these short barrel 5.56s? They are of thinner wall construction and seemingly would open up at lower velocities. Anyone have any idea?

Originally Posted By Funner:This guns purpose is intended for 30 yds and less. At those ranges it will perform flawlessly. It's not a 100yd hunting rifle.

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The 5.56 round is practically harmless unless it fragments. Reliable fragmentation velocity is about 2600 fps.
Your barrel has a muzzle velocity under 1900 fps, which means its effective range is zero meters. You could shoot someone with it point blank in the chest and they'd likely be fine, unless you happened to get lucky and strike the spinal cord. If you had used an 11" barrel, you would probably OK for 30 yards or less...or if you had used a .300 blackout, you'd be fine with that barrel length.

Originally Posted By pebble:The 5.56 round is practically harmless unless it fragments. Reliable fragmentation velocity is about 2600 fps.
Your barrel has a muzzle velocity under 1900 fps, which means its effective range is zero meters. You could shoot someone with it point blank in the chest and they'd likely be fine, unless you happened to get lucky and strike the spinal cord. If you had used an 11" barrel, you would probably OK for 30 yards or less...or if you had used a .300 blackout, you'd be fine with that barrel length.

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Originally Posted By pebble:

Originally Posted By Funner:This guns purpose is intended for 30 yds and less. At those ranges it will perform flawlessly. It's not a 100yd hunting rifle.

The 5.56 round is practically harmless unless it fragments. Reliable fragmentation velocity is about 2600 fps.
Your barrel has a muzzle velocity under 1900 fps, which means its effective range is zero meters. You could shoot someone with it point blank in the chest and they'd likely be fine, unless you happened to get lucky and strike the spinal cord. If you had used an 11" barrel, you would probably OK for 30 yards or less...or if you had used a .300 blackout, you'd be fine with that barrel length.

The 5.56 round is practically harmless unless it fragments. Reliable fragmentation velocity is about 2600 fps.
Your barrel has a muzzle velocity under 1900 fps, which means its effective range is zero meters. You could shoot someone with it point blank in the chest and they'd likely be fine, unless you happened to get lucky and strike the spinal cord. If you had used an 11" barrel, you would probably OK for 30 yards or less...or if you had used a .300 blackout, you'd be fine with that barrel length.

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Yikes! Better not tell the military their 10.5 inch barrels are good to only 30 yards, they will be pretty disappointed.

It's pretty good at poking 5.56 MM holes in stuff. My AR holds about twice as many rounds as my sidearm. If I need to punch a bunch of small holes in something to keep myself safe it seems like a short AR could do that.

Also look into wound channels any hydraulic shock. If you watch a slo mo gel test you can see that the energy transferred is delivered in a wider area than the projectile itself.

The 5.56 round is practically harmless unless it fragments. Reliable fragmentation velocity is about 2600 fps.
Your barrel has a muzzle velocity under 1900 fps, which means its effective range is zero meters. You could shoot someone with it point blank in the chest and they'd likely be fine, unless you happened to get lucky and strike the spinal cord. If you had used an 11" barrel, you would probably OK for 30 yards or less...or if you had used a .300 blackout, you'd be fine with that barrel length.

Originally Posted By codifier:According to the definition of a PDW nothing a civilian can own right now counts; AFAIK the 5.7 and 4.6 offerings came after the Hughes amendment, and PDWs require select fire.

Originally Posted By KnowScot:Also look into wound channels any hydraulic shock. If you watch a slo mo gel test you can see that the energy transferred is delivered in a wider area than the projectile itself.

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Martin Fackler, in his books on would ballistics, concluded that hydraulic shock and temporary wounding cavity was not effective at actually stopping threats.

5.56 out of a barrel this short is pushing the minimum thresholds in the effectiveness of hydrostatic shock (for those that subscribe to the theory).

It isn't just FPS, it is the frontal diameter of the round, it is energy, and more importantly, the transfer of said energy. The are a few .17 caliber rounds in excess of 3600 fps...but they are 20gr. On paper, they may have the necessary fps and energy, but the round (diameter) itself is too small. Example: Take a sharpened pencil and stab a tub of water as hard as you can. Unless your fist hits the water, the thin pencil will not create a big wave. Turn the pencil around and use the eraser side with the force. Slight larger wave. Use a fat magic marker, and even with less force (fps), it will make a bigger wave. Lightly tap the water with a closed fist....you know the rest.

There is a 53gr, hot loaded .223 V-Max round that will expand/fragment down the 1600 fps...but you are still below 500 ft-lbs of energy at the muzzle (generously assuming 2000 fps).

Now, shoot someone enough times with 5.56 out of a barrel that short and it will get the job done...even with FMJ (the blast and concussion would suck no matter what), but there is a reason why 300blk was created, and/or other calibers outside of 5.56 are used for this particular purpose.

In other thread I listed plenty of reasons to use 5.56, even out of a short barrel (ammo is cheap, always available, no threat of cross-loading, etc..)...but ballistics simply isn't one of them. There are better choices available.

Originally Posted By lorazepam:I'm pretty sure hydraulic shock will shut a brain down immediately.

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Early experiments and literature in terminal ballistics never successfully demonstrated any clear relationship between hydraulic shock and incapacitation. There was like one study that showed a connection, but it was contradicted by other studies, and then the research was shut down due to ethical restrictions.

As a result, the conventional school of thought among respected terminal ballistics ever since then, has been that the permanent wound cavity must connect with the CNS -- that is basically brain or spinal cord.

When the 5.56 is traveling below fragmentation velocity, it creates a very small permanent wound cavity. Basically the same as a .22 LR. Can it be lethal? Yes, if you directly hit brain or spinal cord, but this is unlikely given the small area of permanent wound cavity it creates.

It's an amazing round if you get it above fragmentation velocity, because if it fragments, it provides a disproportionately large permanent wound cavity, larger and hence more likely to connect with CNS than a larger caliber.

I have no doubt that enough hydraulic shock could disrupt a heart beat and make them go unconscious, but we simply don't know how to quantify that enough to make informed decisions about ammunition selection based on that method

Originally Posted By pebble:Early experiments and literature in terminal ballistics never successfully demonstrated any clear relationship between hydraulic shock and incapacitation. There was like one study that showed a connection, but it was contradicted by other studies, and then the research was shut down due to ethical restrictions.

As a result, the conventional school of thought among respected terminal ballistics ever since then, has been that the permanent wound cavity must connect with the CNS -- that is basically brain or spinal cord.

When the 5.56 is traveling below fragmentation velocity, it creates a very small permanent wound cavity. Basically the same as a .22 LR. Can it be lethal? Yes, if you directly hit brain or spinal cord, but this is unlikely given the small area of permanent wound cavity it creates.

It's an amazing round if you get it above fragmentation velocity, because if it fragments, it provides a disproportionately large permanent wound cavity, larger and hence more likely to connect with CNS than a larger caliber.

I have no doubt that enough hydraulic shock could disrupt a heart beat and make them go unconscious, but we simply don't know how to quantify that enough to make informed decisions about ammunition selection based on that method

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You can get get yaw/tumble without fragmentation that significantly increases the permanent cavity. It's not as consistent or effective IMO as controlled fragmentation or expansion, but it's not just an ice-pick either.

I won't claim to understand the science behind it, but I have seen gel blocks hit with 5.56 in slo motion. There is a big shockwave that surrounds the projectile. Maybe its not as affective as a JDAM or Hellfire missile, but it sure looks like it is going to cause issues as it travels through a soft pink human body. Remember when we used to kill each other with sticks and clubs? Those worked by transmitting energy to body parts that were not designed to take it. Thats what a bullet from a 5.56 does. If OP needs a super short weapons system, and needs to keep it to standard AR mags for compatibility reasons I say this platform is great.

Probably super loud, a lot of flash, and some other disadvantages, but it has the advantage of ammo, parts, and mag compatibility, and a big advantage on concealment.

Originally Posted By KnowScot:I won't claim to understand the science behind it, but I have seen gel blocks hit with 5.56 in slo motion. There is a big shockwave that surrounds the projectile. Maybe its not as affective as a JDAM or Hellfire missile, but it sure looks like it is going to cause issues as it travels through a soft pink human body. Remember when we used to kill each other with sticks and clubs? Those worked by transmitting energy to body parts that were not designed to take it. Thats what a bullet from a 5.56 does. If OP needs a super short weapons system, and needs to keep it to standard AR mags for compatibility reasons I say this platform is great.

Probably super loud, a lot of flash, and some other disadvantages, but it has the advantage of ammo, parts, and mag compatibility, and a big advantage on concealment.

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Personally I would go 300blk, as the only non-interchangeable part is the barrel, but 5.56 would still do the job if you didn't want to spend 300blk money for blasting ammo.

Originally Posted By KnowScot:I mean...the ammo is not compatable. If OP is working with a partner or a team and someone needs a spare mag I doubt they'd have time to swap barrels.

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While that is a valid reason, I guess I still don't understand how that particular train of thought works with the stated purpose of the weapon.
If it is a PDW, you are probably not working with a partner or a team. How often are civilians with PDW's running out of ammo and/or are working with teams? Or for that matter even actually CARRYING these weapons (in place of, or in conjunction with a sidearm)? Where is it to be used at? In a home, in a car? 5.56 out of a 4.75" barrel in room or hallway? Yikes! If it needs an inches adding muzzle devise to help tame the blast and re-direct the noise, why not just get a longer barrel in a caliber much better suited for short barrels to begin with?

If it is just to punch paper or shoot pumpkins in the field out back, I'll be the first to admit, they look cool as hell. And if that is all you are doing, 5.56 (or even cheaper and less blasty .223) makes far more sense over .300.